Effect of Carbon Addition on Microstructure and Heterogeneous Deformation Behavior of 18%Ni Martensitetic Steel

The effect of carbon on the heterogeneous deformation behavior of a martensite was investigated by multiscale strain distribution analysis using the digital image correlation method. Specially, 18%Ni martensitic steels with and without carbon (0.15C steel and C-free steel, respectively) were studied. Low-magnification observation showed that in both steels, a macroscopic strain distribution was caused by the shape of the specimen. However, high-magnification observation revealed that the strain was concentrated in specific blocks in 0.15C steel, suggesting that its heterogeneous deformation behavior depends on the martensitic structure. Thus, addition of carbon in 18%Ni steel was concluded to cause preferential plastic deformation of the blocks owing to an in-lath plane slip system, which tends to promote heterogeneous deformation.